Investigator will study the efficacy and safety of an inhibitor of intestinal lipase (Orlistat) for reducing serum triglyceride levels in patients with Type I hyperlipoproteinemia. Investigator plan to enroll 20 patients with Type I hyperlipoproteinemia in a randomized, double-blind, placebo-controlled, cross-over trial. During the last week of each study period, fasting blood samples will be drawn for three consecutive days for serum lipids and chemistry panel. The primary endpoint will be serum triglycerides; the secondary endpoint variables will be fasting and postprandial serum chylomicron-TG levels, postprandial serum TG levels during a meal tolerance test and retinyl palmitate levels during a meal tolerance test. Repeated measures analysis of variance will be used for statistical comparisons.